A various conventional hearing aids, designed for hearing impaired persons, have been proposed. However, hearing differs greatly between individuals, and also it is affected from time to time by other factors such as physical condition of a user and his/her sound environment.
Solutions have been addressed to aid hearing impairment in such a way that hearing characteristic of an individual hearing impaired user is measured at specific frequency ranges using an audiometer or the like for example, the result being used to calculate preferable correction and output characteristic for a hearing aid, so that the hearing impaired user can select a hearing aid which provides preferable characteristic (by controlling output for specific frequency ranges) to him/her, or he/she can adjust characteristic on the hearing aid. However, such methods have their own limits because of the difficulty to measure hearing impairment condition or such precisely by using a measuring instrument.
For example, in Japanese published unexamined application No. 2000-165483, because of the possible audible difficulty for a hearing impaired user, a digital phone adjusts its audio output comprising steps including: a step wherein a user parameter, which represents haring spectrum of an individual user, is obtained; a step wherein digital input signal, which represents information heard by a user, is received; a step wherein, in order to generate hearing-adjusted digital signal, digital input signal is adjusted according to the user parameter; and a step wherein analog output signal is generated based on the hearing-adjusted digital signal. However, a special place and highly complicated processes are required in order to obtain hearing characteristic of impaired persons.
Moreover, individual hearing impaired persons would go to various places in their daily lives, which situation requires correction adjustment over output characteristic of a hearing aid, corresponding to sound environment of the place where the user is in, because hearing characteristic is subject to the present sound environment. However, the fact is that there was no such device which can be easily adjusted to the aforementioned situation.
Also, hearing is affected by physical condition of an individual and so on, so that correction over the similar output characteristic to that of the last time may not necessarily work out the best even if the sound environment is the same as before.
Further issue is that hearing is of human aesthesia, so that it is only understood by a hearer and difficult to explain verbally to other people including doctors and specialists. However, in order to measure the hearer's hearing characteristic, his/her personal perception, which cannot be shared with anyone else, needs to be taken out, which is very difficult to do.
An ideal but not realistic solution is a hearing aid being provided with an equalizer, which can adjust input audio corresponding to each user, place, and time, for each user to adjust at the place and time of use of the device. Very possibly this issue would also suffer persons with normal hearing that in noisy environment voice of other people as well as other sounds are hard to hear, resulting in unsmooth conversation, including telephone conversation.
Also one of other demands, in audio field including music listening for example, is for preferable acoustic characteristic which can be adjusted by means of adjusting frequency continuously over various frequency ranges of sound source, corresponding to hearing characteristic of an individual, a place or other factors.
Patent Document 1: Japanese published unexamined application No. 2000-165483